When I do junky inner city urban parks, I disc. out (either mentally/audio by-ears, or via patterns of settings where they are a null disc'd out) : Everything below square tab and downwards.
And then: Skip anything less than 6" deep (varies depending on park and soil-type). Yup, kiss nickels and smaller gold rings goodbye. Yup: Kiss old coins that might-have-been shallow goodbye.
I have had this debate with people who are aghast at not treating junky inner city urban parks in a "relic" or "beach" mindset. They rationalize that: 1) "You might miss a gold ring" and old nickels 2) You might miss an old coin that a gopher pushed to the surface , blah blah.
In other words, they think they can have the "best of all worlds", by being a hero and digging everything that hints of conductive. Eh ? Hard to argue with that, eh ?
But the results are always predictable: They end the day with a pouch of foil, tabs, and clad, and a single wheatie. I end the day with almost no clad, 10 oldies (wheaties/silver), and very little junk. And they simply can not understand why the ratio of oldies is 10 to 1.
If gold rings are someone's agenda, then WHY OH WHY ARE THEY BASHING THEIR BRAINS OUT at junky inner-city blighted urban turf ?
Why not simply go to the beach ? Or sand volley-ball court, or types-of-turf that are more conducive to jewelry ratios/losses ? (spots that are strictly sports related, like soccer fields, ski-lft lines, etc...)
The notion that you can have the "best of all worlds" by being a hero and digging all in blighted turf, is an immediate recipe for the type person where the detector ends up in the closet, and you never hear from them again.